1. Field of the Invention
The present invention relates to a double-chuck mechanical pencil and, more particularly, to a double-chuck mechanical pencil provided with a front chuck for holding a front portion of a lead and a feed chuck disposed behind the front chuck to feed the lead.
2. Description of the Related Art
A double-chuck mechanical pencil is very excellent in reducing the lead loss, i.e., the residual lead that cannot be used. A Conventional double-chuck mechanical pencil has a front chuck, and a feed chuck connected directly to a lead tank. Therefore, if the lead tank is rotated by some cause in a state where a lead is held by both the front chuck and the feed chuck, it is possible that the lead is twisted and broken.
In the double-chuck mechanical pencil, the chucking head of the front chuck is inserted in a forward open end of a barrel. The inside diameter of the forward open end of the barrel is necessarily greater than the outside diameter of the chucking head to ensure the smooth axial movement of the front chuck. Consequently, there is the possibility that the front chuck shakes laterally in the barrel. Therefore, when a color lead more fragile than a black lead is used, the color lead, sometimes, is shook laterally in the barrel and damaged.
The present invention has been made to overcome such disadvantages in the conventional double-chuck mechanical pencil and it is therefore an object of the present invention to provide a double-chuck mechanical pencil having a feed chuck which may not be turned by a lead tank even if the lead tank is turned by some cause.
Another object of the present invention is to provide a double-chuck mechanical pencil having a front chuck that cannot be shook laterally in a barrel.
According to a first aspect of the present invention, a double-chuck mechanical pencil includes a barrel having an open front end part, an inner tube inserted in the barrel, a front chuck having a first chucking head and supported on a front end part of the inner tube with a forward end part of the first chucking head projected outside through the open front end part of the barrel, a feed chuck having a second chucking head inserted in the inner tube, a chuck ring put on the second chucking head of the feed chuck, and a lead tank disposed behind the feed chuck, separated from the feed chuck, capable of axial movement, containing leads and capable of pressing the feed chuck to operate the feed chuck when pressure is applied to the back end thereof.
Preferably, the double-chuck mechanical pencil further includes a first spring interposed between the barrel and the inner tube so as to bias the inner tube continuously backward, a first retaining mechanism associated with the barrel and the inner tube to retain the inner tube on the barrel against the resilience of the first spring, a sleeve inserted in the inner tube and receiving the feed chuck therein with the second chucking head on which the chuck ring is loosely put projecting from the front end of the sleeve, a second spring interposed between the sleeve and the feed chuck to bias the feed chuck backward continuously, a stopping tube disposed behind the sleeve, a second retaining mechanism associated with the inner tube and the stopping tube to retain the stopping tube on the inner tube, and a pushing or pressing member attached to the back end of the lead tank, wherein a front end part of the lead tank is inserted in the stopping tube.
Preferably, the first retaining mechanism includes the barrel provided with axial slots and the inner tube provided with first projections respectively engaging the slots of the barrel, and the second retaining mechanism includes the inner tube provided with slots and the stopping tube provided with second projections respectively engaging the slots of the inner tube.
Preferably, the inner tube has an elastic part capable of axially expanding and contracting to adjust the position of the first projection relative to the slot of the barrel when the respective positions of the slot and the first projection do not coincide.
Preferably, the open front end part of the barrel has a front section having an increased inside diameter, the first chucking head of the front chuck has a plurality of grasping parts each having an angular middle portion and sloping portions having sloping outer surfaces sloping down forward and backward, respectively, from the angular middle portion, and the angular middle portions of the first chucking head of the front chuck lie in the front section having an increased inside diameter of the barrel while the double-chuck mechanical pencil is being used for writing.
Preferably, a metal sleeve having a bore having a front section of an increased inside diameter is fitted in the open front end part of the barrel, the first chucking head of the front chuck has a plurality of grasping parts each having an angular middle portion and sloping portions having sloping outer surfaces sloping down forward and backward, respectively, from the angular middle portion, and the angular portions of the first chucking head of the front chuck lie in the front section having an increased inside diameter of the metal sleeve while the double-chuck mechanical pencil is being used for writing.
Preferably, the metal sleeve is provided with an annular ridge, the open front end part of the barrel is provided with an annular groove, and the metal sleeve is held in the barrel with the annular ridge thereof fitted in the annular groove of the barrel.
Preferably, the double-chuck mechanical pencil further includes a lead holding member interposed between the feed chuck and the front chuck in alignment with the center axis of a lead supply path.
Preferably, the barrel consists of a barrel body and a tip cap attached to a front end part of the barrel body.
Preferably, at least either the feed chuck or the lead tank is provided with an auxiliary pressing means useful for pressing the feed chuck.
Preferably, the auxiliary pressing means is placed on a back end part of the feed chuck or on a front end part of the lead tank.
Preferably, the auxiliary pressing means is a flange.
Preferably, the double-chuck mechanical pencil further includes a third spring capable of exerting a resilient force lower than those that are exerted by the first and the second spring and interposed between the lead tank and the stopping tube.